In the manufacture of semiconductors, semiconductor devices are produced on thin disk-like substrates. Generally, each substrate contains a plurality of semiconductor devices. The exact number of semiconductor devices that can be produced on any single substrate depends both on the size of the substrate and the size of the semiconductor devices being produced thereon. However, semiconductor devices have been becoming more and more miniaturized. As a result of this miniaturization, an increased number of semiconductor devices can be produced for any given area, thus, making the surface area of each substrate more and more valuable.
In producing semiconductor devices, substrates are subjected to a multitude of processing steps before a viable end product can be produced. These processing steps include: chemical-etching, wafer grinding, photoresist stripping, and masking. These steps typically occur in a process tank and often require that each substrate undergo many cycles of cleaning, rinsing, and drying during processing so that particles that may contaminate and cause devices to fail are removed from the substrates. However, these rinsing and drying steps can introduce additional problems in of themselves.
One major problem is the failure of the drying step to completely remove liquid from the substrates after rinsing (or any other processing step where the substrate is exposed to a liquid). It is well known in the art that those semiconductor devices that are produced from an area of the substrate where liquid droplets remained have a greater likelihood of failing. Thus, in order to increase the yield of properly functioning devices per substrate, it is imperative that all liquid be removed from the substrate surface as completely as possible.
Very sophisticated systems and methods have been devised to dry substrates as quickly and as completely as possible. However, due to deficiencies of prior art systems and methods of drying it is impossible to completely remove all traces of liquid from the substrate surfaces in an efficient and inexpensive manner. When substrates are placed in a tank for processing, the substrates are typically supported in an upright position by a support device which can be a carrier or an object support member that is built into the process tank itself. It is a well recognized problem in the art to quickly and effectively remove traces of water from those areas of the substrate that are in contact with the supporting device. Therefore, there is a certain very valuable portion of the substrate which is wasted due to what is known in the art as “edge exclusion,” a term referring to the portion of the substrate near the edges which cannot be completely dried and must be discarded. Because semiconductor devices are becoming more miniaturized, the “edge exclusion” areas are also becoming more valuable in that an increased number of functioning devices would be able to be produced from these areas if it were not for the water-spotting caused by the remaining amounts of liquid.
There have been many attempts to improve dryer systems and drying methods so as to eliminate the need for edge exclusion by completely drying the wafer substrate. However, none have fully solved the problem in an effective and efficient manner.
For example, Mohindra, et al., U.S. Pat. No. 5,571,337, teaches pulsing a drying fluid such as nitrogen gas at the edge of the partially completed semiconductor to remove the liquid from the edge. Application of the Mohindra process results in evaporation of the liquid at the contact points. Evaporation is undesirable because particles or non-purities that may have been present in the water are left behind, both of which decrease yields. Moreover, the equipment necessary to perform the Mohindra process can be expensive and cumbersome.
McConnell, et al., U.S. Pat. No. 4,984,597, teaches using large amounts of IPA to replace water and enhance drying. However, such a process requires special tanks and elaborate support equipment to safely handle and process the IPA. Additionally, the McConnell process is costly due to the large amounts of IPA used.
A third drying system is taught by Munakata in U.S. Pat. No. 6,125,554. Munakata teaches a system for drying substrates comprising a rack having grooves for supporting substrates in a vertical position. The substrates are contacted and supported in the grooves of the rack. Each groove has an aperture near the groove that is capable of sucking water that adheres to the substrate near the groove contact point into the aperture. This system requires additional equipment to create a vacuum force at each groove and the open apertures and cavities within the rack can present problems in a liquid filled process tank because of air bubbles and trapped particles. Additionally, the rack used in Munakata can be both expensive and difficult to manufacture.
Many other systems and methods have been proposed to try to solve the edge exclusion problem resulting from the inability to efficiently remove water residue from the contact points between the edges of substrates and the supporting devices of dryers in a clean, low cost, and timely manner, but none have completely solved the problem.